This section is intended to introduce various aspects of the art, which may be associated with embodiments of the disclosed techniques. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the disclosed techniques. Accordingly, it should be understood that this section is to be read in this light, and not necessarily as admissions of prior art.
Three-dimensional (3D) model construction and visualization have been widely accepted by numerous disciplines as a mechanism for analyzing, communicating, and comprehending complex 3D datasets. Examples of structures that can be subjected to 3D analysis include the earth's subsurface, facility designs and the human body.
3D modeling techniques are important during exploration, development and production phases in the oil and gas industry. For example, reservoir simulation is routinely applied for making development and production strategies to optimize the recovery of hydrocarbon reservoirs that may hold billions of barrels of hydrocarbon fluids.
The ability to easily interrogate and explore 3D models is one aspect of 3D visualization. Relevant models may contain both 3D volumetric objects and co-located 3D polygonal objects. Examples of volumetric objects include seismic volumes, MRI scans, reservoir simulation models, and geologic models. Interpreted horizons, faults and well trajectories are examples of polygonal objects.
3D volumetric objects may be divided into two basic categories: structured grids and unstructured grids. Both structured and unstructured grids may be rendered for a user to explore and understand the associated data. There are large numbers of known volume simulation techniques for structured grids and unstructured grids.
In the oil and gas industry, reservoir simulators exist for operating on structured grids and unstructured grids. Typically, simulators will operate on one grid type or the other, not both.
Structured grid based simulators have been used in the oil industry for several decades and they have been proven to be efficient and stable for industry applications. Unstructured grid based simulators are newer and they have advantages over structured grid based simulators that unstructured grid based simulators can model reservoir internal and external geometries more accurately, and as a result, they give more accurate reservoir performance prediction. Unstructured grid based reservoir simulators are not commercially available. As a result, technical service companies have been trying to rewrite their commercially available structured grid based simulators with unstructured grids for some time. The rewriting process, however, is complicated, time-consuming, and expensive.
In order to convert reservoir models constructed with an unstructured grid so they are usable by structured grid based simulators, workarounds are used. For example, some workarounds involve building a structured grid to mimic the original unstructured grid model to be converted. This process is time consuming and can become very difficult or even impossible when the unstructured grid model is highly faulted and structurally complicated. The situation is worse when there are a lot of history match changes in the unstructured grid reservoir model to be converted. History matching is a process of modifying or tuning the properties of a reservoir model for a better match of the model prediction to observed reservoir production data. The process is to increase the confidence of model prediction. History matching changes on the reservoir properties can be within a cell and on the faces of the cell. An unstructured grid cell (with arbitrary number of faces) generally has more faces than can be handled by a structured grid cell (limited to six faces). As a result, history matching changes cannot be accurately mapped from an unstructured grid to a structured grid, which makes the conversion from the unstructured model to the structured model impossible.
As suggested above, many efforts have been made previously in this area. Among the prior U.S. patents related to the technology disclosed herein, the following non-exclusive list is representative of those efforts: U.S. Pat. Nos. 6,928,399; 7,043,413; 6,106,561; 7,047,165; 6,018,497; 6,078,869; 5,740,342; 7,634,395; 7,451,066; and 7,596,480. International Patent Application Publication No. WO2008150325 is also related to the presently described technologies.